In a preferred embodiment, the present invention concerns a dual band antenna that can provide simultaneous performance in two separate frequency bands. In a particularly preferred embodiment, the dual band antenna of the present invention provides mobile cellular function in both the AMPS (806-890 MHz) and PCS (1850-1990 MHz) frequency bands. Preferably, the antenna is an on-glass style in which energy is directed along a coaxial cable to an on-glass coupler. The coupler transfers energy through the glass of a vehicle, such as an automobile or a truck, to an external radiating element. The radiating element preferably distributes the energy throughout space in a desired radiation pattern. Preferably, the radiating element is designed to provide omni-directional coverage in azimuth.
Known single band mobile cellular antennas can be classified into two categories based upon the gain that they provide.
As shown in FIG. 1, a short, one quarter wavelength stub provides 0 dBd when installed.
As seen in FIG. 2, to increase the antenna gain further, a phasing coil is typically added above the quarter wavelength section. A 1/2 to 5/8.sup.th wavelength long section of wire is then added above the phasing coil. The phasing coil provides a 180 degree phase shift in the current distribution causing the upper and lower sections radiate constructively. Gain is increased to 3 dBd with this technique.
As illustrated in FIGS. 3 and 4, most dual band antennas also fall into two categories.
As seen in FIG. 3, the first category of known dual band antennas is based upon radiators that perform like 1/2 over 1/4 wavelength antennas at high frequencies, while performing like 1/4 wave antennas at low frequencies. This category of antenna provides 3 dBd gain in the high band but only 0 dB gain in the low band.
As seen in FIG. 4, a second category of known dual band antennas is based upon radiators that implement a coaxial choke. These radiators perform in a manner similar to a 1/4 wave antenna at high frequencies, while performance at low frequencies is similar to a 1/2 wave over a 1/4 wave antenna. This second category of antennas provides 0 dBd gain at high frequencies and 3 dBd gain at low frequencies.
Both categories of known dual band antennas provide 3 dBd gain in only one of the two frequency bands.
A principal object of the invention is to provide a dual band antenna capable of simultaneously performing in two separate and distinct bands. Another object is to provide a dual band on-glass antenna capable of simultaneously performing in two separate and distinct bands. A further object is to provide a dual band antenna which delivers 3 dBd of gain in two radiating bands simultaneously via a radiating element that electrically or electromagnetically appears as a 1/2 wavelength over a 1/4 wavelength antenna in both bands.
It is yet another object of the present invention to provide a dual band antenna suitable for simultaneous performance in the PCS and AMPS bands.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.